How do we survive when dinosaurs have gone extinct?
Kamal Lodaya, Bengaluru

It is quite well accepted now that around 6.6 crore years ago, an asteroid at least 10 km in size came from space and crashed at Chicxulub in Mexico. The resulting explosion caused earthquakes, volcanic eruptions, and forest fires throughout the world. The Sun was blotted out by soot and ash to form a long ``winter''. This contributed to the extinction of three-fourths of the plant and animal species living then, including large ones like dinosaurs. We have identified more than a thousand species of dinosaurs which went extinct. It is likely there were a lot more.

The climate then was warm and humid. The level of the oceans was much higher than today. The North and South Poles were not covered with ice sheets like they are now. Forests were widespread, with both flowering and coniferous trees. Daniel Field and colleagues at Bath in England have pieced together what the world looked like after the impact. One of their key ideas was to work with fossil pollen. They find that these forests were destroyed and ferns took over the landscape.

Dinosaurs had feathers, possibly for insulation. They used fluttering to pin down their prey. They used flapping to run up inclines. That different species of dinosaurs evolved flying is not that surprising. There were many kinds of flying dinosaurs, which flew in different ways.

Birds were the only kind of dinosaurs which survived the impact, although many bird species also went extinct. The dinosaurs which were closest in type to birds of today then were raptors like eagles. Earlier it was thought that flight helped these survivors. This was questioned by Derek Larson and colleagues from Canada. For example, all species of toothed birds with claws on ther wings, called {enantiornithes} (``anti-birds''), did not survive. They would have been formidable predators.

Today there are 10,000 species of birds. They may have evolved from a much smaller number which survived. Birds that lived and nested in trees would have felt the worst destruction. Birds which lived on the ground seem to have fared better. Many species could barely fly. Most of their life was on the ground, like today's tinamous, emus, kiwis, or the extinct moa of New Zealand and dodo of Africa. They were timid birds, mostly running away from predators. They were the ancestors of ducks, parrots and chicken. Tinamou are among the oldest birds known. Their fossils from 2 crore years ago have been found. Their biggest threat is human beings hunting and eating them.

BOX: Ustad Mansur and his bird paintings
Ustad Mansur from Emperor Jahangir's court was famous for colour paintings of birds in the early 17th century. In this painting, you can see parrot and pheasant on the top. The extinct dodo bird is in the middle. The goose and sandgrouse are shown at the bottom. He was the earliest artist to paint the dodo in colour and also the first to paint the Siberian crane. He also painted flowers and animals such as the chameleon.
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The Canadian paleontologists think one distinguishing feature of bird species which survived is that they had (and continue to have) toothless beaks. There are species of beaked duck-like birds which did not survive. Abigail Tucker of London thinks the survivors also needed to have gizzards which could digest varied kinds of food. Birds whose meals consisted entirely of insects or small animals may not have made it with all the loss of animal life.

Herbivorous mammals which survived, including our beaver-like ancestors living in burrows, have ever-growing teeth which can continue eating even as they wear down from a continuous diet of plants. The toothless beaks of birds are much simpler, they don't have a jaw. Beaks give the ability to eat hard seeds and nuts.

The beaks may have allowed a different niche for diet in the devastated world after the asteroid impact. The regenerating forests later made this niche into a bonanza for evolving species of birds. They returned to living in trees. As they became smaller, their brains evolved, giving them a pretty good brain size compared to their bodies. Today we know that birds are among the most intelligent species.

Paleontoloigts and author Riley Black writing in the Smithsonian Magazine calls mass extinctions the greatest murder mystery ever known. There are hardly any fossils of birds for nearly 1 crore years after the impact. Finding such fossils will be the key to validating these theories.